This disclosure is directed to a formation tester, and more particularly to a sequential formation tester. As set forth in recent U.S. Pat. No. 4,513,612 issued to the common assignee of the present disclosure, a formation tester is described which incorporates a tool hydraulic system within the body of the formation tester for operation of the tester. The formation tester hydraulic circuit or system incorporates a number of valves important to operation of the formation tester. The formation tester is normally used in adverse environmental circumstances, namely relatively high ambient temperatures and elevated pressures in downhole locations. Moreover, all of the apparatus within the formation tester is exposed to the elevated temperature and is heated by that environment. Ambient bottomhole temperatures significantly impact component operation.
Power for operation of the tool is normally furnished from a power supply conductor in the well logging cable. The well logging cable supports the formation tester at a selected depth in a well borehole for testing, a cable providing electrical power on a set of conductors in the cable. The cable normally is wrapped with a protective sleeve to also enclose signal conductors in the cable. The power demands of the apparatus vary but can be quite high. Peak power demands are often excessive in light of the length of the cable. There typically will be some voltage drop in providing the power necessary to operate the equipment. Moreover, peak power demands typically arise during manipulation of the components of the formation tester. For instance, a snorkel must be extended or retracted. This typically is accomplished by operation of the hydraulic system, such operations requiring power for operation of the various valves in the hydraulic system. These valves are shown in the hydraulic circuit set forth in U.S. Pat. No. 4,513,612. Several different types of valves are required; one of the several valves is a normally closed three way valve. The valve must have power to operate in spite of elevated ambient temperature.
The present apparatus is an improved normally closed four way valve to be used in a formation tester. It is improved by the incorporation of soft seats to enable the valve to seat more readily with a reduced power demand. Recalling that power available in the tool is somewhat limited, peak power demands are reduced by the structure of the present valve.
In many circumstances, it is desirable to incorporate hard valve seats perfecting a seal in conjunction with movable valve elements. However, they must be machined to a quality match to assure proper valve closure. That is, the valve element must seat perfectly on the valve seat to obtain closure. When the valve element and seat are both made of hard materials, certain benefits can be obtained but they are at a cost, namely an increased force required to sustain the valve element closure against the seat.
By contrast, this structure sets forth a normally closed four way valve for use in a formation tester having a soft seat construction. This reduces the peak power demand necessary for valve operation. This enables the formation tester to avoid risk of partial closure, thereby requiring reduced power demand during opening or closing, and also assuring more positive opening and closing of the valve element relative to the valve seat. This particularly is helpful by enabling incorporation of a smaller solenoid, either smaller with reduced number of turns or smaller with a reduced wire size. Moreover, this reduces the current peak required for operation of the solenoid coil moving the valve to the open or closed position. The present valve is designed so that there are pressure dependent forces created in the valve which aid in valve element movement. That is, valve operation is assisted by forces dependent on the hydraulic fluid acting in the valve. This reduces the power required by the solenoid. This assists in closure. Moreover, the soft seat arrangement not only reduces the force required to sustain the closure, it also assists in defining enlarged areas which proportionately convert fluid into valve element operating forces.
One advantage of the present apparatus is the incorporation of a four way normally closed valve for use in a sequential formation tester, the valve incorporating seats which have relatively soft material contacted with the valve element material to enable closure with reduced loading. This valve operates at downhole elevated temperature. Even though the temperature might rise significantly, the valve element and cooperative seat still operate in the same manner and are able to achieve closure without leakage with the incorporation of the soft seat arrangement set forth herein. Other advantages will be more readily apparent upon a consideration of the below included written specification in conjunction with the drawings which follow.